Existing precession-type cameras for taking X-ray diffraction pictures of a crystal include a two-axis mount wherein a pair of frames are journalled for rotation about ganged vertical axes and are connected to a pair of support members that are journalled for rotation about ganged horizontal axes that respectively intersect the ganged vertical axes. The resultant mount is in turn supported for precession about a principal collimation axis of the camera, with the precession angle being determined by the deviation, from such collimation axis, of an elongated element affixed to the mount and extending perpendicular to its horizontal axes.
The crystal whose diffraction pattern is to be recorded is disposed in a holder at the intersection of the collimation axis and the junction of the vertical and horizontal axes in one portion of the mount. In existing designs of this type, the crystal holder, with an associated goniometer head, is fixedly connected to the associated support member of the mount. It has been found that under such circumstances, it is impractical, with a single fixing of the crystal within the camera, to take diffraction pictures in the front-reflection region at precession angles greater than 45 degrees. Moreover, in such systems, the only reciprocal nets that can be recorded are those which are parallel to the main axis of the goniometer head and thereby of the crystal holder.